Seal Structure and Control Method Therefor

ABSTRACT

Provided are a seal structure and a control method therefor that can improve sealing performance between a rotating portion and a fixed portion, smoothly start up a steam turbine, and suppress the temperature rise of the rotating portion even if the rotating portion is continuously rotated for a long period of time. 
     A seal structure is configured such that seal fins  62  on a seal base-plate  61  side and corresponding breathable spacers  4   b  on a rotor  2   a  side are opposed to each other and breathable spacers  4   a  on the seal base-plate  61  side and corresponding seal fins  2   a   1  on the rotor  2   a  side are opposed to each other. The seal base-plate  61  is installed shiftably in a direction coming close to or moving away from the rotor  2   a . If steam St has low pressure, the seal fins  62  and the corresponding breathable spacers  4   b  are not in contact with each other and the seal fins  2   a   1  and the corresponding breathable spacers  4   a  are not in contact with each other. If the steam St has high pressure, the seal fins  62  and the corresponding breathable spacers  4   b  are in contact with each other and the seal fins  2   a   1  and the corresponding breathable spacers  4   a  are in contact with each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seal structure provided for a steamturbine and a control method therefor.

2. Description of the Related Art

For power-generating plants in which a turbine (steam turbine) isrotated for electric generation by steam generated by a steam generatorsuch as a boiler or the like, the steam turbine includes a high-pressureturbine, a medium-pressure turbine and a low-pressure turbine installedin that order from the upstream side of steam flow. The steam havingrotated the low-pressure turbine is introduced via an exhaust hood intoa condenser, in which the steam is condensed as feed-water, which isreturned to the steam generator.

In the steam turbine constituting part of the power-generating plant asdescribed above, a stator blade secured to the inside of a casing isdisposed between rotor blades rotated integrally with a rotor. In thisway, the stator blade and the rotor blade constitute a stage.

The steam introduced into the inside of the casing flows inside thecasing of the steam turbine and expands to rotate the rotor whilealternately passing through between the stator blades and thecorresponding rotor blades secured to the rotor rotatably supported bythe casing. The steam passing a rotor blade installed on the mostdownstream portion of the rotor, i.e., a final-stage rotor blade isdischarged to the outside of the casing.

In the steam turbine as described above, steam impinges on the rotorblade to rotate the rotor. Therefore, to utilize the steam efficiently,it is required to improve sealing performance between a fixed portionand a rotating portion, such as e.g. between the stator blades and therotor, to minimize leakage of steam through a clearance between thefixed portion and the rotating portion.

To deal with such a problem, the following technology of seal structurehas heretofore been disclosed. A labyrinth seal device having fins (sealfins) is disposed between the rotating portion such as a rotor and thefixed portion such as a stator blade. In addition, a member (abradablemetal) superior in the easiness of the abrasion is used at a positionfacing the fin. (See e.g. JP-2002-228013-A). According to the technologydisclosed in JP-2002-228013-A, even if the fin and the abradable metalcome into contact with each other, the fin abrades the abradable metal.Thus, the fin can be prevented from being damaged.

To improve the sealing performance, the fin and the abradable metal aredisposed to reduce the clearance between the rotating portion and thefixed portion as much as possible. In such a case, however, the fin andthe abradable metal often come into contact with each other to increaseresistance (rotational resistance) against the rotation of the rotatingportion. Therefore, when steam has relatively low pressure, for example,such as during the initial period of starting up the steam turbine, therotor becomes hard to be rotated. This poses a problem in that itbecomes difficult to smoothly start up the steam turbine.

Further, for example, the fins provided on the rotating portion and theabradable metal provided on the fixed portion come into contact witheach other to generate frictional heat. This frictional heat istransmitted to the rotating portion, which has high-temperature. Thus,this heat transmission causes thermal deformation of the rotatingportion such as thermal expansion or thermal bending, which affects therotation of the rotating portion. This poses a problem of lowering theturbine efficiency of the steam turbine.

To eliminate such a problem, the technology of a seal structure having athermal insulation layer suppressing the thermal transmission to therotating portion has been disclosed. (See e.g., JP-2007-16704-A).

The technology disclosed in JP-2007-16704-A has a thermal insulationlayer between fins provided on the rotating portion and the rotatingportion, for example. This prevents frictional heat generated by thecontact between the rotating portion and the fixed portion from beingtransmitted to the rotating portion.

SUMMARY OF THE INVENTION

In the technology disclosed in JP-2007-16704-A, however, if the rotatingportion is continuously rotated for a long period of time so that thefins and the abradable metal are in contact with each other for a longperiod of time, the frictional heat thus generated is accumulated in thethermal insulation layer. This poses a problem in that the heataccumulated in the thermal insulation layer is transmitted to therotating portion, which has high-temperature.

When the contact between the fins and the abradable metal increasesrotational resistance and steam pressure is low, the rotor does notrotate smoothly so that the smooth start-up of the steam turbine cannotbe achieved.

If the clearance between the fins and the abradable metal is increasedin order to prevent the contact between the fins and the abradablemetal, the clearance between the rotating portion and the fixed portionis increased to increase the leakage of steam. Thus, it is not probablethat the turbine efficiency of the steam turbine can be improved.

Accordingly, it is an object of the present invention to provide a sealstructure and a control method therefor that can improve sealingperformance between a rotating portion and a fixed portion, smoothlystart up a steam turbine, and suppress the temperature rise of therotating portion even if the rotating portion is continuously rotatedfor a long period of time.

According to an aspect of the present invention, there are provided aseal structure and a control method therefor in which a fin provided ona rotating portion and a spacer provided on a fixed portion are opposedto each other, a fin provided on the fixed portion and a spacer providedon the rotating portion are opposed to each other, the spacers are madeof breathable metal and the fin and the spacer provided on the fixedportion are shiftable in a direction coming close to or moving away fromthe rotating portion.

The aspect of the present invention can provide the seal structure andthe control method therefor that can improve sealing performance betweenthe rotating portion and the fixed portion, smoothly start up a steamturbine, and suppress the temperature rise of the rotating portion evenif the rotating portion is continuously rotated for a long period oftime.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic system diagram of a power-generating plantprovided with a steam turbine according to an embodiment of the presentinvention.

FIG. 2 is a partially enlarged view of the steam turbine of FIG. 1.

FIG. 3 is an enlarged view of an A1-portion of FIG. 2.

FIG. 4 is an enlarged view of an A2-portion of FIG. 3.

FIG. 5A is a cross-sectional view taken along the line X1-X1 in FIG. 2.

FIG. 5B is an enlarged view of an A3-portion of FIG. 5A.

FIG. 6 is a schematic view illustrating one configurational example of ahigh-low labyrinth seal device, in which a seal base-plate is providedwith seal fins.

FIG. 7 is a schematic view illustrating one configurational example of ahigh-low labyrinth seal device, in which a rotor is provided with sealfins.

FIG. 8A is a cross-sectional view taken along the line X2-X2 in FIG. 2.

FIG. 8B is an enlarged view of an A4-portion of FIG. 8A.

FIG. 9 is a schematic view illustrating a distal end of a rotor blade.

FIG. 10 is a schematic view illustrating one configurational example ofa labyrinth seal device equipped with compression springs connectingtogether piston bodies in a circumferential direction.

FIG. 11 is a schematic diagram illustrating one configurational exampleof a labyrinth seal device in which driving steam is allowed to flowinto a pressurizing chamber from a high-pressure steam supply source tothereby move a piston head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will hereinafter be described indetail with reference to the drawings.

Referring to FIG. 1, a power-generating plant 1 is configured to includea boiler 10, a steam turbine 2 (a high-pressure turbine 12, amedium-pressure turbine 14, and a low-pressure turbine 16), a generator18, and a condenser 20. A rotor 2 a of the low-pressure turbine 16 iscoupled to a drive shaft 22 of the generator 18. Rotation of thelow-pressure turbine 16 drives the generator 18 for electric generation.

The boiler 10 is a steam generator, which is provided with a reheater24. The boiler 10 is connected to an inlet side of the high-pressureturbine 12 via a pipe 26. An outlet side of the high-pressure turbine 12is connected to the reheater 24 of the boiler 10 via a pipe 28. Thereheater 24 is connected to an inlet side of the medium-pressure turbine14 via a pipe 30. An outlet side of the medium-pressure turbine 14 isconnected to an inlet side of the low-pressure turbine 16 via a pipe 32.

The pipes 26 and 30 are provided with respective adjusting valves B,each of which functions as a control valve to control an amount of steamSt flowing into a corresponding one of the high-pressure turbine 12 andthe medium-pressure turbine 14. The adjusting valves B are controlled bya controller 54 to control the amount of steam St flowing into thehigh-pressure turbine 12 and the medium-pressure turbine 14.

The steam St generated in the boiler 10 flows into the low-pressureturbine 16 via the high-pressure turbine 12 and the medium-pressureturbine 14 to rotate the rotor 2 a provided in the low-pressure turbine16. The steam St discharged from the low-pressure turbine 16 by therotation of the rotor 2 a passes through an exhaust hood 3 and iscondensed and turned into water (feed-water) in the condenser 20.Thereafter, the feed-water is fed to and heated in the feed-water heater21 and introduced into the boiler 10 or the steam generator via anotherfeed-water heater (not illustrated), a high-pressure feed-water pump(not illustrated) and the like.

Referring to FIG. 2, the steam turbine 2 (e.g. the high-pressure turbine12 illustrated in FIG. 1) includes a plurality of rotor blades 2 bexternally-circumferentially secured to the rotor 2 a and axiallyarranged in a plurality of rows.

Further, the steam turbine 2 includes a casing 2 d embracing the rotor 2a and the rotor blades 2 b, and a plurality of stator blades 2 c securedto the casing 2 d via corresponding nozzle diaphragm outer-rings 80. Theplurality of rotor blades 2 b and the plurality of stator blades 2 c arealternately arranged in the axial direction of the rotor 2 a to formstages.

The externally circumferential direction of the rotor 2 a is hereinafterreferred to as a circumferential direction. That is to say, the rotor 2a is rotated in the circumferential direction.

Steam St generated in the boiler 10 (see FIG. 1) flows into the insideof the casing 2 d of the steam turbine 2. Then, the steam St passesthrough between the stator blades 2 c and the corresponding rotor blades2 b alternately while being reduced in pressure and expanded, therebyrotating the rotor 2 a.

The steam St passing a rotor blade 2 b installed on the most downstreamportion of the rotor 2 a, i.e., a final-stage rotor blade 2 b isdischarged to the outside of the casing 2 d.

In the steam turbine 2 configured as above, to efficiently rotate therotor 2 a by the steam St passing through the inside of the casing 2 d,it is required to improve sealing performance between the rotor 2 a andthe rotor blades 2 b which are a rotating portion and the casing 2 d andthe stator blades 2 c which are a fixed portion to reduce an amount ofsteam St (leakage steam) leaking from the clearance between the rotatingportion and the fixed portion.

For example, to reduce rotational resistance against the rotation of therotor 2 a, a clearance may be provided between a nozzle diaphragminner-ring 70 installed on distal ends of the stator blades 2 c and therotor 2 a in some cases. This clearance causes leakage of steam Stflowing to the stator blades 2 c. The steam St becoming the leakagesteam does not contribute to the rotation of the rotor 2 a. Therefore,the increased amount of leakage steam lowers the turbine efficiency ofthe steam turbine 2. Thus, it is preferable to reduce the amount ofleakage steam in order to improve the turbine efficiency of the steamturbine 2.

For this reason, a configuration is generally employed in which a sealdevice such as a labyrinth seal device 60 is assembled between thenozzle diaphragm inner-ring 70 and the rotor 2 a to reduce the clearancebetween the rotor 2 a and the stator blades 2 c. This configuration canimprove the sealing performance between the rotor 2 a and the statorblades 2 c to thereby reduce the amount of leakage steam.

Referring to FIGS. 3 and 4, the nozzle diaphragm inner-ring 70 accordingto the embodiment is provided on the rotor 2 a side with a sealbase-plate 61 equipped with a plurality of seal fins 62.

The seal base-plate 61 is provided at given intervals with a pluralityof grooves 63 circumferentially formed in line in the axial direction ofthe rotor 2 a. The seal fins 62 are secured to the respective grooves 63by caulking.

Further, also the rotor 2 a is provided at given intervals with aplurality of grooves 2 a 2 circumferentially formed in line in the axialdirection of the rotor 2 a. Seal fins 2 a 1 are secured to therespective grooves 2 a 2 by caulking.

The seal fins 62 on the seal base-plate 61 side and the correspondingseal fins 2 a 1 on the rotor 2 a side are arranged to alternatelyoverlap each other in the axial direction of the rotor 2 a.

As described above, the labyrinth seal device 60 is configured toinclude the seal base-plate 61 provided with the plurality of seal fins62.

In the past, the seal fins 62 on the seal base-plate 61 side and therotor 2 a have been configured so as not to be in contact with eachother. In addition, the seal fins 2 a 1 on the rotor 2 a side and theseal base-plate 61 have been configured so as not to be in contact witheach other. With this configuration, a minute clearance is definedbetween each of the seal fins 62 and the rotor 2 a and between each ofthe seal fins 2 a 1 and the seal base-plate 61, whereby rotationalresistance against the rotation of the rotor 2 a is reduced.

However, steam St passing through these clearances becomes leakage steamwithout contribution to the rotation of the rotor 2 a. The leakage steamcauses a steam leakage loss, which lowers the turbine efficiency of thesteam turbine 2 (see FIG. 1).

For this reason, in the embodiment, a breathable spacer 4 (spacer) madeof breathable metal is attached between each of the seal fins 62 on theseal base-plate 61 side and the rotor 2 a and between each of the sealfins 2 a 1 on the rotor 2 a side and the seal base-plate 61.

Further, the seal base-plate 61 provided with the seal fins 62 and withthe breathable spacers 4 is installed shiftably in a direction comingclose to or moving away from the rotor 2 a, i.e., in therotational-radial direction of the rotor 2 a.

Hereinafter, the breathable spacer 4 on the seal base-plate 61 side isdenoted with reference numeral 4 a and the breathable spacer 4 on therotor 2 a side is denoted with reference numeral 4 b.

With this configuration, the seal fins 62 and the breathable spacers 4 aprovided for the stator blade 2 c (see FIG. 2) which is the fixedportion are shiftable in the direction coming close to and moving awayfrom the rotor 2 a which is the rotating portion.

As illustrated in FIG. 3, the breathable spacers 4 b are attached to therotor 2 a at respective positions opposed to the corresponding seal fins62 on the seal base-plate 61 side.

In addition, the breathable spacers 4 a are attached to the sealbase-plate 61 at respective positions opposed to the corresponding sealfins 2 a 1 on the rotor 2 a side.

This configuration provides a seal structure in which the breathablespacers 4 made of breathable metal are attached to both the rotor 2 a(the rotating portion) and the seal base-plate 61 (the fixed portion).

A method of attaching the breathable spacer 4 to the rotor 2 a and theseal base-plate 61 is not restrictive. For example, the breathablespacer 4 may be secured to the rotor 2 a and the seal base-plate 61 bye.g. brazing.

The breathable spacers 4 b on the rotor 2 a side are eachcircumferentially attached to the outer circumference of the rotor 2 a.In addition, the seal fins 62 on the seal base-plate 61 side and thecorresponding breathable spacers 4 b on the rotor 2 a side areconfigured to be constantly opposed to each other even during therotation of the rotor 2 a. Further, the seal fins 2 a 1 on the rotor 2 aside are provided in the circumferential direction. The seal fins 2 a 1on the rotor 2 a side and the corresponding breathable spacers 4 a onthe seal base-plate 61 side are configured to be opposed to each othereven during the rotation of the rotor 2 a.

Breathable metal used to form the breathable spacer 4 according to thepresent embodiment is a metal material structured such that spaceportions (pores) of porous metal are connected together and gas (steamSt) can pass through the inside thereof. The breathable metal ismaterial (abradable metal) superior in the easiness of the abrasion. Forexample, if the rotor 2 a is rotated in the state where the distal endsof the seal fins 62 on the seal base-plate 61 side are in contact withthe corresponding breathable spacers 4 b on the rotor 2 a side (in thecontact state), the breathable spacers 4 (4 b) are abraded as shown inFIG. 4 but the seal fins 62 are not damaged.

In this way, the configuration in which the distal ends of the seal fins62 come into contact with the respective breathable spacers 4 b on therotor 2 a side can improve the sealing performance between the statorblades 2 c (see FIG. 2) and the rotor 2 a.

Similarly, the configuration in which the distal ends of the seal fins 2a 1 on the rotor 2 a side come into contact with the respectivebreathable spacers 4 a (see FIG. 3) on the seal base-plate 61 side canimprove the sealing performance between the stator blades 2 c and therotor 2 a.

The following technology is a heretofore known one as described earlier.The clearance between the seal fins 62 and the rotor 2 a and between theseal fins 2 a 1 and the seal base-plate 61 is eliminated or made smallto improve the sealing performance between the stator blades 2 c (seeFIG. 2) and the rotor 2 a as shown in FIG. 3. For this purpose, thespacers made of a raw material superior in the easiness of the abrasion,such as e.g. abradable metal are provided on the rotor 2 a at respectivepositions opposed to the corresponding seal fins 62, and on the sealbase-plate 61 at respective positions opposed to the corresponding sealfins 2 a 1.

However, in this technology, frictional heat resulting from frictionbetween the spacers rotating integrally with the rotor 2 a and the sealfins 62, for example, is transmitted to the rotor 2 a, which hashigh-temperature. Thus, the rotor 2 a is thermally deformed such asthermally bent due to e.g. nonuniform temperature distributions so thatthere is a possibility of a problem of causing shaft vibration.

Also, the following technology is thought. A heat-insulating layer madeof a heat-insulating member not illustrated is provided between thespacers on the rotor 2 a side and the rotor 2 a. Even with thistechnology, the rotor 2 a may continuously be rotated for a long periodof time so that the spacers rotated integrally with the rotor 2 a are incontact with the seal fins 62 for a long period of time. In such a case,the frictional heat between the seal fins 62 and the spacers isgradually accumulated so that the heat-insulating layer hashigh-temperature. In this way, the heat of the heat-insulating layer istransmitted to the rotor 2 a, which has high-temperature. Thus, therotor 2 a causes thermal deformation such as thermal bending due tononuniform temperature distributions.

As illustrated in FIG. 4, for example, if the spacer attached to therotor 2 a uses the breathable spacer 4 (4 b) made of breathable metal, aslight amount of steam St passes through the inside of the breathablespacer 4 (4 b).

The steam St passing through the inside of the breathable spacer 4uniformly keeps the breathable spacer 4 at a temperature equal to thatof the steam St. In other words, the breathable spacer 4 will not havetemperature higher than the steam St.

A steam-breathable amount of the breathable spacer 4 has only to be suchan amount as not to affect sealing performance and to be an amount thatuniformly keeps the breathable spacer 4 at a temperature equal to thatof the steam St. The steam-breathable amount of breathable metal used toform the breathable spacer 4 is slight and is a characteristic value ofthe breathable metal depending on the arrangement density and size ofpores. Therefore, it is only necessary to form the breathable spacer 4by using breathable metal that does not affect sealing performance andcan ensure a steam-breathable amount in which an effect is expected ofuniformly keeping the breathable spacer 4 at a temperature equal to thatof the steam St.

As described above, the temperature of the breathable spacer 4 isuniformly kept equally to that of the steam St. The rotor 2 a may berotated for a long period of time so that, for example, the seal fins 62and the breathable spacers 4 b rotated integrally with the rotor 2 a arein contact with each other for a long period of time. Even in such acase, the temperature of the breathable spacers 4 b will not becomehigher than that of the steam St. Thus, an effect is produced in whichthe temperature of the rotor 2 a can be prevented from becoming higherthan that of steam St. The rotor 2 a is designed to have heat resistanceagainst the temperature of steam St. If the temperature of the rotor 2 ais kept at the temperature of the steam St, since e.g. excessive thermalstress and thermal deformation such as thermal bending do not occur, theoperation of the steam turbine 2 (see FIG. 1) is not affected.

Incidentally, the labyrinth seal device 60 illustrated in FIG. 3 may beconfigured such that the breathable spacers 4 are provided on only oneof the rotor 2 a side and the seal base-plate 61 side.

The amount of steam St passing through the breathable spacer 4 asillustrated in FIG. 4 is slighter than that leaking from the clearancebetween the seal fin 62 and the rotor 2 a. Therefore, the amount ofsteam St passing through the breathable spacer 4 does not have aninfluence on the turbine efficiency of the steam turbine 2 (see FIG. 1).

Further, the seal base-plate 61 according to the present embodiment isinstalled shiftably in a direction coming close to or moving away fromthe rotor 2 a.

Referring to FIG. 5A, the nozzle diaphragm inner-ring 70 is provided onthe distal ends of the stator blades 2 c on the inner circumferentialside thereof so as to extend in the circumferential direction. Inaddition, e.g. six seal base-plates 61 equally divided in thecircumferential direction are provided on the end of the nozzlediaphragm inner-ring 70 on the inner circumferential side thereof so asto surround the rotor 2 a.

Referring to FIG. 5B, the seal fins 62 are secured to one sealbase-plate 61 on the rotor 2 a side by caulking or the like so as toextend upright therefrom along the circumferential direction of therotor 2 a. The breathable spacers 4 b made of breathable metal areattached to the outer circumference of the rotor 2 a at respectivepositions opposed to the corresponding seal fins 62.

As illustrated in FIG. 3, the breathable spacers 4 a made of breathablemetal are attached to one seal base-plate 61 at respective positionsopposed to the corresponding seal fins 2 a 1 on the rotor 2 a side so asto be shaped along the circumferential direction.

In the present embodiment, all the seal base-plates 61 are installed onthe nozzle diaphragm inner-ring 70 shiftably in a direction coming closeto or moving away from the rotor 2 a, i.e., in the rotational-radialdirection of the rotor 2 a.

As illustrated in FIG. 3, the nozzle diaphragm inner-ring 70 is formedwith a hollow pressurizing chamber 71. The hollow pressurizing chamber71 is internally provided with a piston head 64 reciprocating in adirection coming close to or moving away from the rotor 2 a. The pistonhead 64 is elastically supported by a plurality of return springs 66(biasing means) circumferentially arranged, e.g., in two lines. Thepiston head 64 is biased at an appropriated biasing force by the returnsprings 66 in a direction moving away from the rotor 2 a.

Incidentally, the number of the return springs 66 may be determinedappropriately.

The pressurizing chamber 71 is configured to communicate with theoutside of the nozzle diaphragm inner-ring 70 through a steam passage72. In addition, steam St flowing through the outside of the nozzlediaphragm inner-ring 70 flows into the pressurizing chamber 71. When thepressure of the steam St is applied to the piston head 64, the pistonhead 64 is shifted in a direction coming close to the rotor 2 a.

The piston head 64 is provided with a piston body 65. The piston body 65extends from the pressurizing chamber 71 toward the rotor 2 a and has anend portion terminating at the outside of the nozzle diaphragminner-ring 70. The seal base-plate 61 is attached to the end portion.

The piston body 65 may be formed integrally with the piston head 64, forexample. A method of attaching the seal base-plate 61 to the piston body65 is not restrictive. For example, the seal base-plate 61 may besecured to the piston body 65 by means of screws not illustrated.

Thus, a movable portion is configured to include the piston head 64, thepiston body 65, and the seal base-plate 61.

When the piston head 64 is supported by the biasing force of the returnsprings 66 at a position away from the rotor 2 a, the seal base-plate 61is in a state shifted to a position away from the rotor 2 a. In thisstate, the seal fins 62 on the seal base-plate 61 side are not incontact with the corresponding breathable spacers 4 b, opposed thereto,on the rotor 2 a side (the non-contact state). Thus, a clearance isdefined between the seal fins 62 and the corresponding breathablespacers 4 b.

Similarly, the seal fins 2 a 1 on the rotor 2 a side are not in contactwith the corresponding breathable spacers 4 a, opposed thereto, on theseal base-plate 61 side. In this state, a clearance is defined betweenthe seal fins 2 a 1 and the corresponding breathable spacers 4 a.

The labyrinth seal device 60 in the present embodiment is configured toinclude the pressurizing chamber 71, the steam passage 72, the pistonhead 64, the piston body 65, and the return springs 66 in addition tothe seal base-plate 61.

The seal structure including the labyrinth seal device 60 and the sealfins 2 a 1 and breathable spacers 4 b on the rotor 2 a side is assembledinto the steam turbine 2 (see FIG. 1).

After the steam St generated in the boiler 10 (see FIG. 1) flows intothe steam turbine 2, when the steam St passes through between the statorblades 2 c and the rotor blades 2 b, a portion of the steam St passesthrough the steam passage 72 and flows into the pressurizing chamber 71.

Force (pressing force) adapted to shift the piston head 64 in adirection coming close to the rotor 2 a results from the pressure of thesteam St flowing into the pressurizing chamber 71. If this force issmaller than the biasing force of the plurality of return springs 66,the return springs 66 support the piston head 64 at a position away fromthe rotor 2 a.

For example, if a load connected to the steam turbine 2 (see FIG. 1) isincreased so that the pressure of the steam St flowing through the steamturbine 2 is increased, also the pressure of the steam St flowing intothe pressurizing chamber 71 is increased. The pressing force, resultingfrom the pressure of the steam St, adapted to shift the piston head 64in the direction coming close to the rotor 2 a becomes equal to orgreater than the biasing force of the return springs 66. At this time,the piston head 64 is shifted by the pressure of the steam St in thedirection coming close to the rotor 2 a. In addition, the sealbase-plate 61 connected to the piston head 64 via the piston body 65 isshifted in the direction coming close to the rotor 2 a.

When the piston head 64, in the pressurizing chamber 71, is shifted to astop position on the side close to the rotor 2 a, the seal fins 62 onthe seal base-plate 61 side come into contact with the correspondingbreathable spacers 4 b on the rotor 2 a side. With this configuration,if the pressure of the steam St flowing into the pressurizing chamber 71is increased, the seal fins 62 and the corresponding breathable spacers4 b opposed thereto come into contact with each other. Thus, theclearance between the seal fins 62 and the corresponding breathablespacers 4 b can be eliminated, thereby improving the sealing performancebetween the stator blades 2 c (see FIG. 2) and the rotor 2 a.

Similarly, when the piston head 64, in the pressurizing chamber 71, isshifted to the stop position on the side close to the rotor 2 a, thebreathable spacers 4 a on the seal base-plate 61 side come into contactwith the corresponding seal fins 2 a 1 on the rotor 2 a side. With thisconfiguration, if the pressure of the steam St flowing into thepressurizing chamber 71 is increased, the breathable spacers 4 a comeinto contact with the corresponding seal fins 2 a 1 opposed thereto,thereby improving the sealing performance between the stator blades 2 c(see FIG. 2) and the rotor 2 a.

As described above, the seal fins 62 on the seal base-plate 61 side arein contact with the corresponding breathable spacers 4 b on the rotor 2a side and the seal fins 2 a 1 on the rotor 2 a side are in contact withthe corresponding breathable spacers 4 a on the seal base-plate 61 side.In this case, rotational resistance against the rotation of the rotor 2a is increased; however, if the pressure of the steam St is high, therotor 2 a can be rotated against the rotational resistance increased bythe contact between the seal fins 62 and the corresponding breathablespacers 4 b and between the seal fins 2 a 1 and the correspondingbreathable spacers 4 a. That is to say, the rotor 2 a can be rotatedwithout the influence of the rotational resistance increased by thecontact between the seal fins 62 and the corresponding breathablespacers 4 and between the seal fins 2 a 1 and the correspondingbreathable spacers 4.

In other words, it is only necessary for the biasing force of theplurality of return springs 66 to be set so that the piston head 64 canbe shifted in the direction coming close to the rotor 2 a by thepressure of the steam St that can rotate the rotor 2 a withoutundergoing an influence of the rotational resistance increased by thecontact between the seal fins 62 and the corresponding breathablespacers 4 b and between the seal fins 2 a 1 and the correspondingbreathable spacers 4 a.

Incidentally, the steam St flowing through the inside of the steamturbine 2 (see FIG. 1) expands and reduces in pressure from the upstreamtoward the downstream. Therefore, the return springs 66 installed in thelabyrinth seal device 60 of the stator blade 2 c may be configured tohave respective biasing forces that are gradually decreased as the flowof the steam St goes toward the downstream side.

The labyrinth seal device 60 may be such that the number of the sealbase-plates 61 is not limited to six but seven or more seal base-plates61 are provided along the circumferential direction. Alternatively, thelabyrinth seal device 60 may be provided with five or less sealbase-plates 61 along the circumferential direction.

In the steam turbine 2 (see FIG. 1) into which the seal structureconfigured as described above is assembled, during the initial period ofstart-up low in the pressure of steam St, the seal fins 62 on the sealbase-plate 61 side are not in contact with the corresponding breathablespacers 4 b on the rotor 2 a side. In addition, the seal fins 2 a 1 onthe rotor 2 a side are not in contact with the corresponding breathablespacers 4 a on the seal base-plate 61 side.

In this way, the rotational resistance against the rotation of the rotor2 a is reduced so that the rotor 2 a is efficiently rotated by the steamSt at low pressure.

If the load of the steam turbine 2 (see FIG. 1) is increased to increasethe pressure of the steam St, the seal fins 62 are in contact with thecorresponding breathable spacers 4 b and the seal fins 2 a 1 are incontact with the corresponding breathable spacers 4 a. In this way, thesealing performance between the stator blades 2 c (see FIG. 2) and therotor 2 a is improved. Thus, the turbine efficiency of the steam turbine2 is improved.

The steam St with high pressure can efficiently rotate the rotor 2 awithout undergoing an influence of the rotational resistance increasedby the contact between the seal fins 62 and the corresponding breathablespacers 4 b and between the seal fins 2 a 1 and the correspondingbreathable spacers 4 a.

That is to say, during the initial period of start-up or the like in thesteam turbine 2 (see FIG. 1), when the pressure of the steam St isrelatively low, the seal fins 62 on the seal base-plate 61 side are notin contact with the corresponding breathable spacers 4 b on the rotor 2a side and the seal fins 2 a 1 on the rotor 2 a side are not in contactwith the corresponding breathable spacers 4 a on the seal base-plate 61side. In this way, the rotational resistance against the rotation of therotor 2 a is reduced. Thus, the rotor 2 a is efficiently rotated by thesteam St with low pressure, thereby smoothly starting up the steamturbine 2.

When the steam turbine 2 (see FIG. 1) is increased in load to increasethe pressure of steam St, the seal fins 62 on the seal base-plate 61side come into contact with the corresponding breathable spacers 4 b onthe rotor 2 a side and the seal fins 2 a 1 on the rotor 2 a side comeinto contact with the corresponding breathable spacers 4 a on the sealbase-plate 61 side. In this way, the amount of leakage steam between thestator blades 2 c (see FIG. 2) and the rotor 2 a is reduced, therebyimproving the turbine efficiency.

The description has thus so far been given of the followingconfigurational examples. In one of them, the plurality of breathablespacers 4 are attached to the rotor 2 a and the labyrinth seal device60. In the other one, the seal base-plate 61 constituting part of thelabyrinth seal device 60 is provided on the nozzle diaphragm inner-ring70 so as to be shiftable in the direction coming close to or moving awayfrom the rotor 2 a. However, the configuration of the invention is notlimited to these.

Examples of the labyrinth seal device 60 include a high-low labyrinthseal device in addition to the device shaped as illustrated in FIG. 3.The present invention can be applied to also the high-low labyrinth sealdevice.

Referring to FIG. 6, a high-low labyrinth seal device 60 a is providedwith a seal base-plate 61 on a nozzle diaphragm inner-ring 70. The sealbase-plate 61 is provided with seal fins 62 projecting upright along thecircumferential direction and shiftably in a direction coming close toor moving away from a rotor 2 a. The rotor 2 a is formed with projectingportions 2 a 3 along the circumferential direction on the outercircumference thereof. The seal fins 62 on the seal base-plate 61 sideare each arranged to face a corresponding one of the projecting portions2 a 3 and recessed portions 2 a 4 of the rotor 2 a, each of the recessedportions 2 a 4 being formed between the projecting portions 2 a 3.

Further, the labyrinth seal device 60 a is configured to include apressurizing chamber 71, a steam passage 72, a piston head 64, a pistonbody 65, and a plurality of return springs 66 circumferentially arrangedin two lines.

As illustrated in FIG. 6, breathable spacers 4 b are attached to thecorresponding projecting portions 2 a 3 and recessed portions 2 a 4formed on the rotor 2 a so as to face the corresponding seal fins 62 onthe seal base-plate 61 side.

The attachment of the breathable spacers 4 b as described above canimprove the sealing performance between the stator blades 2 c (see FIG.2) and the rotor 2 a.

A seal structure including the labyrinth seal device 60 a and thebreathable spacers 4 b on the rotor 2 a side are assembled into thesteam turbine 2 (see FIG. 1).

Incidentally, the high-low labyrinth seal device 60 a illustrated inFIG. 6 may be configured such that the breathable spacers 4 b areattached to either one of the projecting portions 2 a 3 and recessedportions 2 a 4 of the rotor 2 a.

Also in the high-low labyrinth seal device 60 a, the seal base-plate 61can be installed on the nozzle diaphragm inner-ring 70 shiftably in adirection coming close to or moving away from the rotor 2 a.

With this configuration, the seal fins 62 provided on the stator blade 2c (see FIG. 2) which is a fixed portion can be shiftable in a directioncoming close to or moving away from the rotor 2 a which is a rotatingportion.

Similarly to the configuration illustrated in FIG. 3, steam St passesthrough the steam passage 72 and flows into the pressurizing chamber 71.The pressure of the steam St may be high and a pressing force adapted toshift the piston head 64 in a direction coming close to the rotor 2 amay be equal to or greater than the biasing force of the plurality ofreturn springs 66. In such a case, the piston head 64 is shifted in thedirection coming close to the rotor 2 a so that the seal base-plate 61operating integrally with the piston head 64 via the piston body 65 isshifted in the direction coming close to the rotor 2 a.

When the piston head 64, in the pressurizing chamber 71, is shifted to astop position on the side close to the rotor 2 a, the seal fins 62 onthe seal base-plate 61 side come into contact with the correspondingbreathable spacers 4 b attached to the corresponding projecting portions2 a 3 and recessed portions 2 a 4 of the rotor 2 a. With thisconfiguration, when the pressure of the steam St flowing into thepressurizing chamber 71 is high, the seal fins 62 on the seal base-plate61 side come into contact with the corresponding breathable spacers 4 battached to the projecting portions 2 a 3 and recessed portions 2 a 4 ofthe rotor 2 a. In this contact state, a clearance between the seal fins62 and the corresponding breathable spacers 4 b is eliminated, therebyimproving the sealing performance between the stator blades 2 c (seeFIG. 2) and the rotor 2 a.

As illustrated in FIG. 7, a high-low labyrinth seal device 60 b may beacceptable in which a plurality of seal fins 2 a 5 are provided on theouter circumference of a rotor 2 a.

In this case, a seal base-plate 61 a is formed with a plurality ofprojecting portions 61 a ₁ and a plurality of recessed portions 61 a ₂which are circumferentially formed to be lined in the axial direction ofthe rotor 2 a. In addition, breathable spacers 4 a shaped along thecircumferential direction are attached to the plurality of correspondingprojecting portions 61 a ₁ and recessed portions 61 a ₂.

The labyrinth seal device 60 b is configured to include the sealbase-plate 61 a attached with the breathable spacers 4 a, a pressurizingchamber 71, a steam passage 72, a piston head 64, a piston body 65, anda plurality of return springs 66 arranged e.g. in the circumferentialdirection in two lines.

Further, the rotor 2 a is provided on the outer circumference with theseal fins 2 a 5 which are provided upright along the circumferentialdirection at respective positions opposed to the correspondingprojecting portions 61 a ₁ and recessed portions 61 a ₂ of the sealbase-plate 61 a.

A seal structure including the labyrinth seal device 60 b and the sealfins 2 a 5 on the rotor 2 a side are assembled into the steam turbine 2(see FIG. 1).

Also in the high-low labyrinth seal device 60 b, the seal base-plate 61a can be installed on the nozzle diaphragm inner-ring 70 shiftably in adirection coming close to or moving away from the rotor 2 a.

With this configuration, the breathable spacers 4 a provided on thestator blade 2 c (see FIG. 2) which is a fixed portion can be shiftablein a direction coming close to or moving away from the rotor 2 a whichis a rotating portion.

Similarly to the labyrinth seal device 60 illustrated in FIG. 3, steamSt passes through the steam passage 72 and flows into the pressurizingchamber 71. The pressure of the steam St may be high and a pressingforce adapted to shift the piston head 64 in a direction coming close tothe rotor 2 a may be equal to or greater than the biasing force of theplurality of return springs 66. In such a case, the piston head 64 isshifted in the direction coming close to the rotor 2 a so that the sealbase-plate 61 a operating integrally with the piston head 64 via thepiston body 65 is shifted in the direction coming close to the rotor 2a.

When the piston head 64, in the pressurizing chamber 71, is shifted to astop position on the side close to the rotor 2 a, the breathable spacers4 a on the seal base-plate 61 a side come into contact with thecorresponding seal fins 2 a 5 on the rotor 2 a side. With thisconfiguration, when the pressure of the steam St flowing into thepressurizing chamber 71 is high, the breathable spacers 4 a on the sealbase-plate 61 a side come into contact with the corresponding seal fins2 a 5 on the rotor 2 a side. In this contact state, a clearance betweenthe breathable spacers 4 a and the corresponding seal fins 2 a 5 iseliminated, thereby improving the sealing performance between the statorblades 2 c (see FIG. 2) and the rotor 2 a.

As described above, the labyrinth seal device 60 b can be configuredsuch that the high-low seal base-plate 61 a is provided on the nozzlediaphragm inner-ring 70 shiftably in the direction coming close to ormoving away from the rotor 2 a. Thus, the labyrinth seal device 60 b canproduce the same effect as that of the labyrinth seal device 60illustrated in FIG. 3.

The present embodiment can be applied to a labyrinth seal deviceinstalled between the nozzle diaphragm outer-ring 80 (see FIG. 2) andthe rotor blades 2 b (see FIG. 2).

Referring to FIG. 8A, a cover 2 g is provided at the distal ends of therotor blades 2 b to reduce the clearance between the rotor blades 2 band the nozzle diaphragm outer-ring 80 (see FIG. 2). As illustrated inFIG. 8B, the cover 2 g is provided with a plurality of seal fins 2 g 1.

As illustrated in FIG. 8A, the cover 2 g is provided at the distal endsof the rotor blades 2 b so as to extend circumferentially annularly. Inaddition, the seal fins 2 g 1 (see FIG. 8B) are provided on the cover 2g so as to extend upright along the circumferential direction.

Seal base-plates 91 are installed on the nozzle diaphragm outer-ring 80so as to face the cover 2 g provided on the rotor blades 2 b.

The nozzle diaphragm outer-ring 80 on the rotor blade 2 b side is formedto extend in the circumferential direction. In addition, e.g. six sealbase-plates 91 equally divided in the circumferential direction areinstalled between the nozzle diaphragm outer-ring 80 and the rotorblades 2 b so as to surround the rotor blades 2 b.

As illustrated in FIG. 8B, breathable spacers 4 a are circumferentiallyattached to one seal base-plate 91 on the rotor blade 2 b side. Inaddition, the seal fins 2 g 1 are provided on the cover 2 g atrespective positions opposed to the corresponding breathable spacers 4a.

In the present embodiment, all the seal base-plates 91 are installed onthe nozzle diaphragm outer-ring 80 shiftable in a direction coming closeto or moving away from the rotor blades 2 b, i.e., in therotational-radial direction of the rotor blades 2 b.

Referring to FIG. 9, the seal base-plate 91 is of e.g. a high-low-type.Specifically, the seal base-plate 91 is formed with a plurality ofprojecting portions 91 a and a plurality of recessed portions 91 b. Theprojecting portions 91 a and the recessed portions 91 b are shaped toextend along the rotational direction of the rotor blade 2 b, i.e., inthe circumferential direction and are formed in line in the axialdirection of the rotor 2 a (see FIG. 2). The breathable spacers 4 a areattached to the corresponding projecting portions 91 a and recessedportions 91 b so as to be shaped in the circumferential direction.

With this configuration, the breathable spacers 4 a provided for thecasing 2 d (see FIG. 2) which is a fixed portion can be shifted in adirection coming close to or moving away from the rotor blade 2 b whichis a rotating portion.

The Seal fins 2 g 1 are circumferentially installed on the cover 2 g ofthe rotor blade 2 b to extend upright at respective positions opposed tothe corresponding projecting portions 91 a and recessed portions 91 b ofthe seal base-plate 91.

The nozzle diaphragm outer-ring 80 is provided with a hollowpressurizing chamber 81. The hollow pressurizing chamber 81 isinternally provided with a piston head 92 reciprocating in a directioncoming close to or moving away from the rotor blade 2 b. The piston head92 is elastically supported by a plurality of return springs 94 (biasingmeans) circumferentially arranged, e.g., in two lines. In this way, thepiston head 92 is biased by the return springs 94 in a direction movingaway from the rotor blade 2 b.

Incidentally, the number of the return springs 94 may be setappropriately.

The pressurizing chamber 81 is configured to communicate with theoutside of the nozzle diaphragm outer-ring 80 through a steam passage82. Steam St flowing through the outside of the nozzle diaphragmouter-ring 80 flows into the pressurizing chamber 81. When the pressureof the steam St is applied to the piston head 92, the piston head 92 isshifted in a direction coming close to the rotor blade 2 b.

The piston head 92 is provided with a piston body 93. The piston body 93extends from the pressurizing chamber 81 toward the rotor blade 2 b andhas an end portion terminating at the outside of the nozzle diaphragmouter-ring 80. The seal base-plate 91 is attached to the end portion.

The piston body 93 may be formed integrally with the piston head 92, forexample. A method of attaching the seal base-plate 91 to the piston body93 is not restrictive. For example, the seal base-plate 91 may besecured to the piston body 93 by means of screws not illustrated.

Thus, a movable portion is configured to include the piston head 92, thepiston body 93, and the seal base-plate 91.

The labyrinth seal device 90 in the present embodiment is configured toinclude the seal base-plate 91, the piston head 92, the piston body 93,the plurality of return springs 94, the pressurizing chamber 81, and thesteam passage 82.

A seal structure including the labyrinth seal device 90 and the sealfins 2 g 1 on the rotor blade 2 b side is assembled into the steamturbine 2 (see FIG. 1).

When the piston head 92 of the labyrinth seal device 90 is supported bythe biasing force of the return springs 94 at a position away from therotor blade 2 b, the seal base-plate 91 is shifted to a position awayfrom the rotor blade 2 b. In this state, the breathable spacers 4 a onthe seal base-plate 91 side are not in contact with the correspondingseal fins 2 g 1, opposed thereto, on the cover 2 g side of the rotorblades 2 b. Thus, a clearance is defined between the breathable spacers4 a and the corresponding seal fins 2 g 1.

After the steam St generated in the boiler 10 (see FIG. 1) flows intothe steam turbine 2 (see FIG. 1), when the steam St passes through theoutside of the nozzle diaphragm outer-ring 80, a portion of the steam Stpasses through the steam passage 82 and flows into the pressurizingchamber 81.

The pressure of the steam St flowing into the pressurizing chamber 81causes a pressing force adapted to shift the piston head 92 in adirection coming close to the rotor blade 2 b. If this pressing force issmaller than the biasing force of the plurality of return springs 94,the return springs 94 support the piston head 92 at a position away fromthe rotor blade 2 b.

When the piston head 92 is supported at a position away from the rotorblade 2 b by the biasing force of the return springs 94, the sealbase-plate 91 is shifted to a position away from the rotor blade 2 b. Inthis state, the breathable spacers 4 a on the seal base-plate 91 sideare not in contact with the corresponding seal fins 2 g 1, opposedthereto, on the cover 2 g side of the rotor blade 2 b. Thus, a clearanceis defined between the breathable spacers 4 a and the corresponding sealfins 2 g 1.

If the pressure of the steam St flowing into the steam turbine 2 (seeFIG. 1) is increased, also the pressure of the steam St flowing into thepressurizing chamber 81 is increased. The pressure of the steam Stcauses a pressing force adapted to shift the piston head 92 in thedirection coming close to the rotor blade 2 b. If this pressing forcebecomes equal to or greater than the biasing force of the return springs94, the piston head 92 is shifted in the direction coming close to therotor blade 2 b by the pressure of the steam St. In addition, the sealbase-plate 91 connected to the piston head 92 via the piston body 93 isshifted in the direction coming close to the rotor blade 2 b.

When the piston head 92, in the pressurizing chamber 81, is shifted to astop position on the side close to the rotor blade 2 b, the breathablespacers 4 a on the seal base-plate 91 side come into contact with thecorresponding seal fins 2 g 1 on the cover 2 g side of the rotor blades2 b. With this configuration, if the pressure of the steam St flowinginto the pressurizing chamber 81 is increased, the breathable spacers 4a on the seal base-plate 91 side come into contact with thecorresponding seal fins 2 g 1 on the cover 2 g side of the rotor blades2 b. Consequently, the clearance between the seal fins 2 g 1 and thecorresponding breathable spacers 4 a can be eliminated. Thus, thesealing performance between the nozzle diaphragm outer-ring 80 and therotor blades 2 b is improved.

Similarly to the labyrinth seal device 60 illustrated in FIG. 3, it isonly necessary for the biasing force of the plurality of return springs94 to be set so that the piston head 92 can be shifted in the directioncoming close to the rotor blade 2 b by the pressure of the steam St thatcan rotate the rotor 2 a without undergoing an influence of therotational resistance increased by the contact between the seal fins 2 g1 and the breathable spacers 4 a.

The steam St flowing through the inside of the steam turbine 2 (seeFIG. 1) expands and reduces in pressure from the upstream toward thedownstream. Therefore, similarly to the labyrinth seal device 60illustrated in FIG. 3, the return springs 94 may be configured to haverespective biasing forces that are gradually decreased as the flow ofthe steam St goes toward the downstream side.

The number of the seal base plates 91 is not limited to six. Thelabyrinth seal device 90 circumferentially provided with seven or moreseal base-plates 91 may be acceptable. Alternatively, the labyrinth sealdevice 90 circumferentially provided with five or less seal base-plates91 may be acceptable.

In the steam turbine 2 (see FIG. 1) including the labyrinth seal device90 and the seal fins 2 g 1 on the cover 2 g side of the rotor blades 2 billustrated in FIG. 9, during the initial period of start-up relativelylow in the pressure of steam St, the breathable spacers 4 a on the sealbase-plate 91 side are not in contact with the corresponding seal fins 2g 1 on the cover 2 g side of the rotor blade 2 b. A clearance is definedbetween the breathable spacers 4 a and the corresponding seal fins 2 g 1so that the rotational resistance against the rotation of the rotorblade 2 b (the rotating portion) is reduced. The rotor 2 a isefficiently rotated by the steam St with low pressure to smoothly startup the steam turbine 2.

When the steam turbine 2 (see FIG. 1) is increased in load to increasethe pressure of steam St, the breathable spacers 4 a on the sealbase-plate 91 side come into contact with the seal fins 2 g 1 on thecover 2 g side of the rotor blades 2 b to eliminate the clearancebetween the breathable spacers 4 a and the corresponding seal fins 2 g1. In this way, the sealing performance between the nozzle diaphragmouter-ring 80 and the rotor blades 2 b is improved. Thus, an amount ofleakage steam occurring between the nozzle diaphragm outer-ring 80 andthe rotor blades 2 b is reduced to thereby improve the turbineefficiency of the steam turbine 2.

Incidentally, the labyrinth seal device 90 illustrated in FIG. 9 isconfigured such that the plurality of breathable spacers 4 a areattached to the seal base-plate 91 and the plurality of seal fins 2 g 1are provided on the cover 2 g. However, the labyrinth seal device 90 maybe configured such that the seal fins are provided on the sealbase-plate 91 and the breathable spacers are attached to the cover 2 g.

Alternatively, the labyrinth seal device 90 may be configured such thatthe plurality of seal fins are provided on both the seal base-plate 91and the cover 2 g. In this case, the breathable spacers are configuredto be attached to the cover 2 g at respective positions opposed to thecorresponding seal fins on the seal base-plate 91 side and to the sealbase-plate 91 at respective positions opposed to the corresponding sealfins on the cover 2 g side.

The embodiments of the present invention have been described thus far.However, the invention is not limited to the embodiments described aboveand can appropriately be modified in design in a range not departingfrom the gist of the invention.

In the labyrinth seal device 60 illustrated in FIG. 3, the sealbase-plate 61 is biased by the return springs 66 elastically supportingthe piston head 64 in the pressurizing chamber 71 in the directionmoving away from the rotor 2 a. However, for example, respective pistonbodies 65 of adjacent seal base-plates 61 may circumferentially beconnected to each other via compression springs 66 a (biasing means) asillustrated in FIG. 10.

The compression springs 66 a are installed between the adjacent pistonbodies 65 in a compressed state so as to bias the piston body 65 in adirection moving the adjacent piston bodies 65 away from each other.

One piston body 65 is elastically supported by the compression springs66 a in a state shifted to a position away from the rotor 2 a. The sealbase-plate 61 is attached to the piston body 65 so that the sealbase-plate 61 is supported at a position away from the rotor 2 a.

When steam St (see FIG. 3) flows into the pressurizing chamber 71, thepressure of the steam St causes a pressing force adapted to shift thepiston head 64 in a direction coming close to the rotor 2 a. If thispressing force exceeds the biasing force of the compression springs 66a, the piston head 64 is shifted in a direction coming close to therotor 2 a. As the piston head 64 is shifted, the seal base-plate 61 isshifted in a direction coming close to the rotor 2 a.

Thus, the same effect as that of the labyrinth seal device 60illustrated in FIG. 3 is produced.

The labyrinth seal device 60 illustrated in FIG. 3 is configured suchthat the piston head 64 is driven by the pressure of the steam Stflowing through the steam turbine 2 (see FIG. 1). For example, thefollowing configuration illustrated in FIG. 11 may be acceptable. Thepiston head 64 is shifted in a direction coming close to the rotor 2 aby the high pressure of steam (driving steam) for driving the pistonhead 64, the steam flowing into the pressurizing chamber 71 from ahigh-pressure steam supply source 102.

A labyrinth seal device 60 c illustrated in FIG. 11 is configured toinclude a valve control device 100, an operating condition detectingdevice 101, the high-pressure steam supply source 102, and anelectromagnetic valve 103 in addition to the labyrinth seal device 60illustrated in FIG. 3.

A seal structure including the labyrinth seal device 60 c and theplurality of seal fins 2 a 1 and plurality of breathable spacers 4 b onthe rotor 2 a 1 side is assembled into the steam turbine 2 (see FIG. 1).

The high-pressure steam supply source 102 is connected to thepressurizing chamber 71 via the electromagnetic valve 103. Further, thevalve control device 100 for controlling the opening/closing of theelectromagnetic valve 103 is provided.

Preferably, the valve control device 100 is configured to control theopening/closing of the electromagnetic valve 103 on the basis of theoperating condition of the steam turbine 2 (see FIG. 1). The valvecontrol device 100 is provided with the operating condition detectingdevice 101 for detecting the operating condition of the steam turbine 2.

With this configuration, the valve control device 100 can shift amovable portion including the piston head 64, the piston body 65, andthe seal base-plate 61 in a direction coming close to the rotor 2 a onthe basis of the operating condition of the steam turbine 2.

A drive device is configured to include the pressurizing chamber 71, thevalve control device 100, the high-pressure steam supply source 102, andthe electromagnetic valve 103.

Preferably, the operating condition of the steam turbine 2 (see FIG. 2)is detected based on e.g. the rotation speed of the rotor 2 a. Theoperating condition detecting device 101 is a rotation speed detectingdevice for detecting the rotation speed of the rotor 2 a.

The operating condition detecting device which is the rotation speeddetecting device detects the rotation speed of the rotor 2 a andconverts it to a detection signal, which is sent to the valve controldevice 100.

The valve control device 100 calculates the rotation speed of the rotor2 a on the basis of the detection signal supplied from the operatingcondition detecting device 101 (the rotation speed detecting device).

If the calculated rotation speed of the rotor 2 a is smaller than apredetermined rotation speed, the valve control device 100 sends acontrol signal to the electromagnetic valve 103 for closing.

The predetermined rotation speed in this case may appropriately setbased on the performance or the like of the steam turbine 2 (see FIG.1).

The electromagnetic valve 103 is closed based on a control signal sentfrom the valve control device 100 to cut off the inflow of driving steamto the pressurizing chamber 71 from the high-pressure steam supplysource 102.

When the driving steam does not flow into the pressurizing chamber 71,the piston head 64 is shifted by the biasing force of the return springs66 in a direction moving away from the rotor 2 a.

When the piston head 64 is shifted in the direction moving away from therotor 2 a, the seal base-plate 61 is shifted in the direction movingaway from the rotor 2 a. In this way, the seal fins 62 on the sealbase-plate 61 side are not in contact with the corresponding breathablespacers 4 b on the rotor 2 a side. In addition, the breathable spacers 4a on the seal base-plate 61 side are not in contact with thecorresponding seal fins 2 a 1 on the rotor 2 a side. Thus, rotationalresistance against the rotation of the rotor 2 a is reduced.

If the calculated rotation speed of the rotor 2 a is equal to or higherthan the predetermined rotation speed, the valve control device 100sends a control signal to the electromagnetic valve 103 for opening.

The electromagnetic valve 103 is opened based on the control signal sentfrom the valve control device 100, so that the driving steam flows intothe pressurizing chamber 71 from the high-pressure steam supply source102.

The piston head 64 is shifted in a direction coming close to the rotor 2a by the pressure of the driving steam flowing into the pressurizingchamber 71 from the high-pressure steam supply source 102.

When the piston head 64 is shifted in the direction coming close to therotor 2 a, the seal base-plate 61 is shifted in the direction comingclose to the rotor 2 a. In this way, the seal fins 62 on the sealbase-plate 61 side come into contact with the corresponding breathablespacers 4 b on the rotor 2 a side. In addition, the seal fins 2 a 1 onthe rotor 2 a side come into contact with the corresponding breathablespacers 4 a on the seal base-plate 61 side.

Thus, the sealing performance between the stator blades 2 c (see FIG. 2)and the rotor 2 a is improved.

If the rotation speed of the rotor 2 a is low e.g. during the initialperiod of starting up the steam turbine 2 (see FIG. 1), the valvecontrol device 100 closes the electromagnetic valve 103 to bring theseal fins 62 on the seal base-plate 61 side and the correspondingbreathable spacers 4 b on the rotor 2 a side into non-contact with eachother. In addition, the seal fins 2 a 1 on the rotor 2 a side and thecorresponding breathable spacers 4 a on the seal base-plate 61 side arebrought into non-contact with each other. In this way, the rotationalresistance against the rotation of the rotor 2 a is reduced. Thus, therotor 2 a is efficiently rotated by the steam St and the steam turbine 2is smoothly started up.

When the steam turbine 2 (see FIG. 1) is started up and the rotationspeed of the rotor 2 a is increased, the valve control device 100 opensthe electromagnetic valve 103 to bring the seal fins 62 on the sealbase-plate 61 side and the corresponding breathable spacers 4 b on therotor 2 a side into contact with each other. In addition, the seal fins2 a 1 on the rotor 2 a side and the corresponding breathable spacers 4 aon the seal base-plate 61 side are brought into contact with each other.

Thus, the steam turbine 2 is improved in the sealing performance betweenthe stator blades 2 c (see FIG. 2) and the rotor 2 a, thereby improvingturbine efficiency.

Preferably, the pressure of the driving steam is pressure that can shiftthe piston head 64 in a direction coming close to the rotor 2 a againstthe biasing force of the return springs 66.

A configuration may be acceptable in which the operating condition ofthe steam turbine 2 is detected by use of e.g. the pressure of the steamSt. In this case, the operating condition detecting device 101 is apressure detecting device for detecting the pressure of the steam St.

The operating condition detecting device 101 which is the pressuredetecting device detects the pressure of steam St flowing through thesteam turbine 2 (see FIG. 1) and sends a detection signal to the valvecontrol device 100. The valve control device 100 calculates the pressureof the steam St.

If the pressure of the steam St is lower than a predetermined pressurevalue, the valve control device 100 sends a control signal to theelectromagnetic valve 103 for closing.

The electromagnetic valve 103 is closed based on the control signal sentfrom the valve control device 100 to cut off the inflow of the drivingsteam to the pressurizing chamber 71 from the high-pressure steam supplysource 102.

It is only necessary for the predetermined pressure value to beappropriately set based on the performance or the like of the steamturbine 2 (see FIG. 1).

If the driving steam does not flow into the pressurizing chamber 71, thepiston head 64 is shifted in a direction moving away from the rotor 2 aby the biasing force of the return springs 66.

When the piston head 64 is shifted in the direction moving away from therotor 2 a, the seal base-plate 61 is shifted in the direction movingaway from the rotor 2 a. In this way, the seal fins 62 on the sealbase-plate 61 side and the corresponding breathable spacers 4 b on therotor 2 a side are not in contact with each other. In addition, thebreathable spacers 4 a on the seal base-plate 61 side, and thecorresponding seal fins 2 a 1 on the rotor 2 a side are not in contactwith each other. Thus, the rotational resistance against the rotation ofthe rotor 2 a is reduced.

If the pressure of the steam St is equal to or greater than thepredetermined pressure value, the valve control device 100 sends acontrol signal to the electromagnetic valve 103 for opening.

The electromagnetic valve 103 is opened based on the control signal sentfrom the valve control device 100, so that the driving steam flows intothe pressurizing chamber 71 from the high-pressure steam supply source102.

The piston head 64 is shifted in a direction coming close to the rotor 2a by the pressure of the driving steam flowing into the pressurizingchamber 71 from the high-pressure steam supply source 102.

When the piston head 64 is shifted in the direction coming close to therotor 2 a, the seal base-plate 61 is shifted in the direction comingclose to the rotor 2 a. In this way, the seal fins 62 on the sealbase-plate 61 side and the corresponding breathable spacers 4 b on therotor 2 a side come into contact with each other. In addition, the sealfins 2 a 1 on the rotor 2 a side and the corresponding breathablespacers 4 a on the seal base-plate 61 side come into contact with eachother.

Thus, the sealing performance between the stator blades 2 c (see FIG. 2)and the rotor 2 a is improved.

When the pressure of the steam St is lower than the predeterminedpressure value, e.g., during the initial period of starting up the steamturbine 2 (see FIG. 1), the valve control device 100 closes theelectromagnetic valve 103. In this way, the seal fins 62 on the sealbase-plate 61 side and the corresponding breathable spacers 4 b on therotor 2 a side are brought into non-contact with each other. Inaddition, the seal fins 2 a 1 on the rotor 2 a side and thecorresponding breathable spacers 4 a on the seal base-plate 61 side arebrought into non-contact with each other. This reduces the rotationalresistance against the rotation of the rotor 2 a. Thus, the rotor 2 a isefficiently rotated by the steam St with low-pressure and the steamturbine 2 is smoothly started up.

The steam turbine 2 (see FIG. 2) is started up and the pressure of thesteam St becomes equal to or greater than the predetermined pressurevalue. Then, the valve control device 100 opens the electromagneticvalve 103 to bring the seal fins 62 on the seal base-plate 61 side andthe corresponding breathable spacers 4 b on the rotor 2 a side intocontact with each other. In addition, this brings the seal fins 2 a 1 onthe rotor 2 a side and the corresponding breathable spacers 4 a on theseal base-plate 61 side into contact with each other.

The steam turbine 2 is improved in the sealing performance between thestator blades 2 c (see FIG. 2) and the rotor 2 a, thereby improvingturbine efficiency.

That is to say, when the pressure of the steam St is lower than thepredetermined pressure value, such as during the initial period ofstart-up or the like, the steam turbine 2 (see FIG. 2) is such that theclearance is defined between the stator blades 2 c (see FIG. 2) and therotor 2 a. This reduces rotational resistance against the rotation ofthe rotor 2 a, so that the rotor 2 a is efficiently rotated by the steamSt for smooth start-up. When the pressure of the steam St becomes equalto or greater than the predetermined pressure value, the steam turbine 2is improved in the sealing performance between the stator blades 2 c(see FIG. 2) and the rotor 2 a, thereby improving turbine efficiency.

Incidentally, the labyrinth seal device 60 c illustrated in FIG. 11 isconfigured such that the driving steam is allowed to flow into thepressurizing chamber 71 from the high-pressure steam supply source 102to shift the piston head 64 in a direction coming close to the rotor 2a. However, a configuration may be acceptable in which the piston head64 is shifted in a direction coming close to the rotor 2 a by a drivingmeans such as an actuator or the like not illustrated.

The seal structure (see FIG. 9) assembled between the nozzle diaphragmouter-ring 80 and the rotor blades 2 b may be made to have the sameconfiguration as that of the seal structure illustrated in FIG. 11.

As described above, the steam turbine 2 (see FIG. 1) according to thepresent embodiment has the seal structure assembled between the statorblades 2 c (see FIG. 2) which are the fixed portion and the rotor 2 awhich is the rotating portion, the seal structure including thelabyrinth seal device 60, the seal fins 2 a 1 on the rotor 2 a side, andthe breathable spacers 4 b on the rotor 2 a side, as illustrated in FIG.3.

In addition, the seal fins 62 on the seal base-plate 61 side of thelabyrinth seal device 60 come into contact with the correspondingbreathable spacers 4 b on the rotor 2 a side and the seal fins 2 a 1 onthe rotor 2 a side come into contact with the corresponding breathablespacers 4 a on the seal base-plate 61 side. This configuration improvesthe sealing performance between the stator blades 2 c and the rotor 2 a,thereby producing an excellent effect of suppressing the lowering ofturbine efficiency due to leakage steam.

Further, the breathable spacer 4 (4 a, 4 b) is formed of breathablemetal which is abradable material superior in the easiness of theabrasion. With this configuration, even if the seal fin 62 and the sealfin 2 a 1 each come into contact with the breathable spacer 4, thebreathable spacer 4 is abraded. Therefore, an excellent effect isproduced in which the seal fin 62 and the seal fin 2 a 1 are preventedfrom being damaged.

The breathable spacer 4 made of breathable metal can aerate a slightamount of steam St. Therefore, frictional heat resulting from thecontact between each of the seal fins 62 and 2 a 1 and the breathablespacer 4 can be cooled by the steam St passing through the breathablespacer 4. Thus, the breathable spacer 4 can be prevented from havingtemperature higher than that of the steam St.

For example, also even if the rotor 2 a is rotated for a long period oftime and the seal fins 62 and 2 a 1 and the breathable spacer 4 causefrictional heat for a long period of time, the breathable spacer 4 willnot have temperature higher than that of the steam St. The rotor 2 a andthe seal base-plate 61 each of which is attached with the breathablespacer 4 do not have temperature higher than that of the steam St. Thus,an excellent effect can be produced in which the rotor 2 a and the sealbase-plate 61 are prevented from causing thermal deformation.

For example, the spacer made of porous metal is abradable materialsuperior in the easiness of the abrasion. If the seal fins 62 and 2 a 1each come into contact with the spacer made of porous metal, since thespacer made of porous metal is abraded, the seal fins 62 and 2 a 1 canbe prevented from being damaged.

However, pores of the porous metal may sometimes not communicate witheach other. In such a case, the spacer made of porous metal cannotaerate steam St. Thus, the frictional heat caused by the contact betweeneach of the seal fins 62 and 2 a 1 and the spacer made of porous metalcannot be cooled by the steam St.

In the present embodiment, because of the provision of the breathablespacer 4 made of breathable metal, the frictional heat caused by thecontact between each of the seal fins 62 and 2 a 1 and the breathablespacer 4 can be cooled by the steam St passing through the breathablespacer 4.

The seal base-plate 61 provided with the seal fins 62 and the breathablespacers 4 a is installed on the nozzle diaphragm inner-ring 70 shiftablyin a direction coming close to or moving away from the rotor 2 a. Whenthe steam St has low pressure, the seal fins 62 on the seal base-plate61 side and the corresponding breathable spacers 4 b on the rotor 2 aside are not in contact with each other. In addition, the seal fins 2 a1 on the rotor 2 a side and the corresponding breathable spacers 4 a onthe seal base-plate 61 side are not in contact with each other.

With this configuration, when the steam St has low pressure, such ase.g. during the initial period of starting up the steam turbine 2 (seeFIG. 1), the seal fins 62 and 2 a 1 are not in contact with thecorresponding breathable spacers 4. This can reduce the rotationalresistance against the rotation of the rotor 2 a. Thus, even if thepressure of the steam St is low, the rotor 2 a can efficiently berotated, thereby producing an excellent effect of smoothly starting upthe steam turbine 2.

When the load of the steam turbine 2 is increased to increase thepressure of the steam St, the seal fins 62 and 2 a 1 are brought intocontact with the corresponding breathable spacers 4. This can improvethe sealing performance between the stator blades 2 c (see FIG. 2) andthe rotor 2 a. Thus, an excellent effect of preventing the lowering ofthe turbine efficiency of the steam turbine 2 can be produced.

Incidentally, the seal structure including the labyrinth seal device 60,the plurality of seal fins 2 a 1, and the plurality of breathablespacers 4 b illustrated in e.g. FIG. 3 can be assembled not only betweenthe nozzle diaphragm inner-ring 70 and the rotor 2 a but also betweenanother fixed portion and another rotating portion such as between thecasing 2 d (see FIG. 2) and the rotor 2 a.

Even a labyrinth seal device 60 in which the seal fins 62 and breathablespacers 4 a on the fixed portion side are installed so as not to beshifted in a direction coming close to or moving away from the rotatingportion can produce a cooling effect resulting from the breathablespacers 4 aerating the steam St.

1. A seal structure assembled into a steam turbine including a rotatingportion composed of a rotor and a member rotating integrally with therotor, and a fixed portion composed of a casing embracing the rotatingportion and a member secured to the casing, the seal structurecomprising: a seal fin provided on both or either one of the rotatingportion and the fixed portion, wherein if the seal fin is provided onthe fixed portion, a spacer made of breathable metal is provided on therotating portion so as to oppose to the seal fin provided on the fixedportion, the seal fin provided on the fixed portion can be shifted in adirection coming close to or moving away from the rotating portion, andif the seal fin is provided on the rotating portion, a spacer made ofbreathable metal is provided on the fixed portion so as to oppose to theseal fin provided on the rotating portion, the spacer provided on thefixed portion can be shifted in a direction coming close to or movingaway from the rotating portion.
 2. The seal structure according to claim1, wherein the member secured to the casing is a stator blade providedon the casing, the seal fin is provided at both or either one of adistal end of the stator blade and a portion, of the rotor, opposed tothe distal end of the stator blade, if the seal fin is provided at thedistal end of the stator blade, the spacer is provided on the rotor soas to oppose to the seal fin provided at the distal end of the statorblade, the seal fin provided at the distal end of the stator blade canbe shifted in a direction coming close to or moving away from the rotor,and if the seal fin is provided on the rotor, the spacer is provided atthe distal end of the stator blade so as to oppose to the seal finprovided on the rotor, the spacer provided at the distal end of thestator blade can be shifted in a direction coming close to or movingaway from the rotor.
 3. The seal structure according to claim 1, whereinthe member rotating integrally with the rotor is a rotor blade providedon the rotor, the seal fin is provided at both or either one of aportion, of the casing, opposed to a distal end of the rotor blade andthe distal end of the rotor blade, if the seal fin is provided on thecasing, the spacer is provided at the distal end of the rotor blade soas to oppose to the seal fin provided on the casing, the seal finprovided on the casing can be shifted in a direction coming close to ormoving away from the distal end of the rotor blade, and if the seal finis provided at the distal end of the rotor blade, the spacer is providedon the casing so as to oppose to the seal fin provided at the distal endof the rotor blade, the spacer provided on the casing can be shifted ina direction coming close to or moving away from the distal end of therotor blade.
 4. The seal structure according to any one of claims 1 to 3wherein the fixed portion is provided with a movable portion biased bybiasing means in a direction moving away from the rotating portion, andbeing shiftable in a direction coming close to the rotating portion bypressure of steam flowing through the steam turbine, if the seal fin isprovided on the fixed portion, the seal fin provided on the fixedportion is attached to the movable portion, if the spacer is provided onthe fixed portion, the spacer provided on the fixed portion is attachedto the movable portion, when a pressing force, resulting from thepressure of the steam, adapted to shift the movable portion in adirection coming close to the rotating portion is smaller than a biasingforce, of the biasing means, adapted to bias the movable portion in adirection moving away from the rotating portion, the movable portion isshifted to a position away from the rotating portion, so that the sealfin and the spacer opposed thereto are not in contact with each other,and when the pressing force is equal to or greater than the biasingforce, the movable portion is shifted to a position close to therotating portion, so that the seal fin and the spacer opposed theretocome into contact with each other.
 5. The seal structure according toany one of claims 1 to 3, wherein the fixed portion is provided with amovable portion biased by biasing means in a direction moving away fromthe rotating portion, and being shiftable in a direction coming close tothe rotating portion, if the seal fin is provided on the fixed portion,the seal fin provided on the fixed portion is attached to the movableportion, if the spacer is provided on the fixed portion, the spacerprovided on the fixed portion is attached to the movable portion, theseal structure further includes an operating condition detecting devicefor detecting an operating condition of the steam turbine, and a drivedevice for shifting the movable portion in a direction coming close tothe rotating portion, and on the basis of the operating condition of thesteam turbine detected by the operating condition detecting device, thedrive device shifts the movable portion in a direction coming close tothe rotating portion to bring the seal fin and the spacer opposedthereto into contact with each other.
 6. The seal structure according toclaim 5, wherein the operating condition detecting device is a rotationspeed detecting device for detecting rotation speed of the rotor anddetects the operating condition of the steam turbine through therotation speed of the rotor, and the drive device shifts the movableportion in a direction coming close to the rotating portion when therotation speed of the rotor is equal to or higher than a predeterminedrotation speed.
 7. The seal structure according to claim 5, wherein theoperating condition detecting device is a pressure detecting device fordetecting pressure of steam flowing through the steam turbine anddetects the operating condition of the steam turbine through thepressure of the steam, and the drive device shifts the movable portionin a direction coming close to the rotating portion when the pressure ofthe steam is equal to or greater than a predetermined pressure value. 8.A control method for a seal structure assembled into a steam turbineincluding a rotating portion composed of a rotor and a member rotatingintegrally with the rotor, and a fixed portion composed of a casingembracing the rotating portion and a member secured to the casing, theseal structure including: a seal fin provided on both or either one ofthe rotating portion and the fixed portion, wherein the fixed portion isprovided with a movable portion biased by biasing means in a directionmoving away from the rotating portion, and being shiftable in adirection coming close to the rotating portion by a drive device, if theseal fin is provided on the fixed portion, a spacer made of breathablemetal is provided on the rotating portion so as to oppose to the sealfin provided on the fixed portion, the seal fin provided on the fixedportion is attached to the movable portion, and if the seal fin isprovided on the rotating portion, a spacer made of breathable metal isprovided on the fixed portion so as to oppose to the seal fin providedon the rotating portion, the spacer provided on the fixed portion isattached to the movable portion, the control method comprising the stepsof: detecting rotation speed of the rotating portion; and shifting themovable portion in a direction coming close to the rotating portion whenthe rotation speed of the rotating portion is equal to or higher than apredetermined rotation speed; wherein when the rotation speed of therotating portion is equal to or higher than the predetermined rotationspeed, the seal fin and the spacer opposed thereto are brought intocontact with each other.
 9. A control method for a seal structureassembled into a steam turbine including a rotating portion composed ofa rotor and a member rotating integrally with the rotor, and a fixedportion composed of a casing embracing the rotating portion and a membersecured to the casing, the seal structure including: a seal fin providedon both or either one of the rotating portion and the fixed portion,wherein the fixed portion is provided with a movable portion biased bybiasing means in a direction moving away from the rotating portion, andbeing shiftable in a direction coming close to the rotating portion by adrive device, if the seal fin is provided on the fixed portion, a spacermade of breathable metal is provided on the rotating portion so as tooppose to the seal fin provided on the fixed portion, the seal finprovided on the fixed portion is attached to the movable portion, and ifthe seal fin is provided on the rotating portion, a spacer made ofbreathable metal is provided on the fixed portion so as to oppose to theseal fin provided on the rotating portion, the spacer provided on thefixed portion is attached to the movable portion, the control methodcomprising the steps of: detecting pressure of steam flowing through thesteam turbine, and shifting the movable portion in a direction comingclose to the rotating portion when the pressure of the steam is equal toor greater than a predetermined pressure value; wherein when thepressure of the steam is equal to or greater than the predeterminedpressure value, the seal fin and the spacer opposed thereto are broughtinto contact with each other.